Photographer spent eight days in cave to make a viral video.

The biggest cavern in Vietnam's Son Doong Cave is so vast that it could accommodate a Boeing 747. “You feel absolutely miniscule,” says Ryan Deboodt, a professional photographer whose video of the cave went viral this week. Deboodt spent eight days camped inside the cave, one of the world's largest, with a GoPro fitted onto a drone.

Your film really captures the enormous scale of the cave. How did you do that?

It was just being sure to have people in the shots—without people you just don’t really know. It’s just having the people down low. It’s sometimes difficult to even see them, but when you do, it makes it that much bigger. You realize, “Oh, wow, that’s somebody tiny right there.”

You used a quadcopter to get the footage. What exactly is that?

It’s a remote-controlled helicopter with four rotors, and there’s a GoPro on the bottom.

Inside the caves there’s no GPS, so it’s flown on manual, and it takes a bit more to make sure it doesn’t run into anything. [Laughs] You can actually get quite strong drafts—when clouds are forming inside the cave, the drafts are so strong that you can see them blow a cloud through.

What lives inside the cave?

Under the skylights, you have spiders, you have birds, you have all kinds of bugs and snakes. In the dark parts of the cave, you have species of fish and a translucent wood louse, which have evolved to no longer have pigments because they’re in darkness all the time.

The [trees] are tall and very skinny because they’re reaching up for the light. So they don’t grow very wide; they just grow up and up.

Since the cave is in a national park, is it pretty well protected?

There’s still a bit of deforestation in the park, and the Bru-Vân Kiều [an ethnic group that lives in the park] still depend on [the land for farming]. But I’m fully on the conservation side. That’s one of the things I wanted to do with this video: to show how beautiful it is, and how it should be protected.

You’ve done a lot of photography with caves. What is it about them that inspires you?

For me, caves are one of the last unexplored places in the world. It’s that draw of exploration, of being somewhere no one else has been, seeing things that no one else has seen.

This interview has been edited and condensed. Follow Ralph Martins on Twitter.

Explore the 2.5-mile Hang Son Doong, or “mountain river cave,” along the Vietnam-Laos border via this animated 3-D flyby.